First, studies are continuing of the L2C leukemia of inbred strain 2 guinea pigs. It has been previously demonstrated that the tumor specific transplantation antigen (TSTA) is only immunogenic when guinea pigs are immunized with an Ia positive variant of the leukemia. A soluble KCl extract has been prepared from L2C cells that is also highly protective. Studies are now in progress to identify the molecular species of the TSTA in the KCl extract. Recent evidence suggests that the immunogenic molecule has a M.W. of 20,000. Allo and autoantibodies have also been prepared which react with an idiotype present on an IgM surface molecule but not with Ia antigen molecules on the cell surface. Second, we are investigating suppressor lymphocytes of humans generated by concanavalin A activation. Such suppressor cells have been demonstrated to be T cells that reside in a fraction of particular buoyant density. Suppressor cells can be generated in the absence of proliferation. Suppressor T cell activity has also been studied in ten patients with systemic lupus erythematosis (SLE). The majority of these patients had defects in the generation of suppressor cells. BIBLIOGRAPHIC REFERENCE: Konen, T.G., Green, I., Shevach, E.M., Kask, A.M. and Schwartz, B.D.: Mutant lines of guinea pig L2C leukemia. III. The reaction of an alloantiserum detecting idiotypic determinants on a clonally derived guinea pig B cell leukemia with IgM and Ia molecules. J. Immunol. 117: 1966, 1976.